Annular solenoid with axially overlapping electromagnet and armature

ABSTRACT

An electromagnetic actuator having an annular pole piece and an annular armature with surfaces formed thereon through which a magnetic flux passes. One of the annular pole piece and the annular armature is axially movable relative to the other between a first position, in which the surfaces are spaced axially apart by a minimum distance, and a second position in which the surfaces are spaced axially apart by a maximum distance. The surfaces axially overlap one another but do not touch when the one of the annular pole piece and the annular armature is positioned in the first position and in the second position.

This is a divisional application of U.S. Ser. No. 11/507,311 filed Aug. 21, 2006, the disclosure of which is hereby incorporated by reference as if fully set forth in detail herein.

INTRODUCTION

The present disclosure generally relates to an annular solenoid with axially overlapping electromagnet and armature.

It is known in the vehicle axle art to employ an electromagnetic actuator to translate members of an assembly into/out of engagement with one another. For example, commonly owned U.S. Pat. No. 6,958,030 discloses an electromagnetic locking differential assembly that employs an electromagnetic actuator to selectively couple a side gear to a differential case to cause the differential assembly to operate in a fully locked condition. More specifically, the electromagnetic actuator is actuated to axially translate an actuating ring (which is non-rotatably coupled to the differential case) such that dogs on the actuating ring matingly engage dogs that are formed on a face of the side gear opposite the gear teeth. As another example, U.S. Patent Application Publication No. 2004/0132572 discloses an electromagnetic locking differential assembly that employs an electromagnetic actuator to selectively operate a ball ramp plate to lock a side gear to a differential case so that the differential operated in a fully locked condition.

SUMMARY

In one form, the present teachings provide an electromagnetic actuator with an electromagnet and an annular armature. The electromagnet has an annular coil and an annular shell. The annular coil is formed of a plurality of windings that are disposed about a circumference of the annular coil. The annular shell is disposed about the annular coil and comprises a first frusto-conically shaped surface. The annular armature comprises a second frusto-conically shaped surface. One of the electromagnet and the annular armature is axially movable relative to the other one of the electromagnet and the annular armature between a first position, in which the first and second frusto-conically shaped surfaces are spaced axially apart by a maximum distance, and a second position in which the first and second frusto-conically shaped surfaces are spaced axially apart by a minimum distance. The first and second frusto-conically shaped surfaces axially overlap but do not touch one another when the one of the electromagnet and the annular armature is in the first position and when the one of the electromagnet and the annular armature is in the second position.

In another form, the present teachings provide an electromagnetic actuator with a coil assembly and an annular armature. The coil assembly has an annular coil and an annular pole piece. The annular coil is formed of a plurality of windings that are disposed about a circumference of the annular coil. The annular pole piece is disposed about the annular coil and comprises a first surface. The annular armature comprises a second surface. One of the coil assembly and the annular armature is axially movable relative to the other one of the coil assembly and the annular armature between a first position, in which the first and second surfaces are spaced axially apart by a maximum distance, and a second position in which the first and second surfaces are spaced axially apart by a minimum distance. The first and second surfaces axially overlap but do not touching one another when the one of the coil assembly and the annular armature is in the first position and when the one of the coil assembly and the annular armature is in the second position.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a front view of an actuator assembly constructed in accordance with the teachings of the present disclosure;

FIG. 2 is a side elevation of the actuator assembly of FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is a front view of a portion of the actuator assembly of FIG. 1 illustrating the frame in more detail;

FIG. 5 is a section view taken along the line 5-5 of FIG. 4;

FIG. 6 is a partial side elevation view of the frame;

FIG. 7 is a front view of a portion of the actuator assembly of FIG. 1 illustrating the outer shell in more detail;

FIG. 8 is a sectional view taken along the line 8-8 of FIG. 7;

FIG. 9 is a perspective view of a portion of the actuator assembly of FIG. 1 illustrating the inner shell in more detail;

FIG. 10 is a longitudinal section view of the inner shell;

FIG. 11 is a front view of a portion of the actuator assembly of FIG. 1 illustrating the coil in more detail;

FIG. 12 is a sectional view taken along the line 12-12 of FIG. 11;

FIG. 13 is a longitudinal sectional view of a portion of the actuator assembly of FIG. 1 illustrating the armature in more detail;

FIG. 14 is an enlarged portion of FIG. 13;

FIG. 15 is a perspective view of a portion of the actuator assembly of FIG. 1 illustrating the plunger in more detail;

FIG. 16 is a sectional view taken along the line 16-16 of FIG. 1;

FIG. 17 is a schematic sectional view of a portion of the sensor assembly;

FIG. 18 is a plot illustrating the output of the sensor signal produced by the sensor assembly as a function of the relative position of the sensor target;

FIG. 19 is a schematic illustration of the coil assembly and sensor assembly as coupled to a power source and a controller;

FIG. 20 is an elevation view illustrating the calibration of the sensor assembly after the actuator assembly of FIG. 1 has been assembled;

FIG. 20A is a front view of another actuator assembly constructed in accordance with the teachings of the present disclosure, the actuator including a sensor assembly having redundant sensor portions;

FIG. 21 is a schematic illustration of a vehicle having a driveline constructed in accordance with the teachings of the present disclosure;

FIG. 22 is a partially broken away perspective view of a portion of the vehicle of FIG. 21, illustrating the rear axle assembly in more detail;

FIG. 23 is an exploded perspective view of a portion of the rear axle assembly, illustrating the differential assembly in more detail;

FIG. 24 is a partially broken away perspective view of the differential assembly;

FIG. 25 is an exploded perspective view of a portion of the rear axle assembly, illustrating the differential assembly in more detail;

FIG. 26 is a front view of another actuator assembly constructed in accordance with the teachings of the present disclosure;

FIG. 27 is a sectional view taken along the line 27-27 of FIG. 26;

FIG. 28 is a side elevation of the actuator assembly of FIG. 26;

FIG. 29 is a partial perspective view of a portion of an alternatively constructed plunger; and

FIGS. 30 through 32 are partial schematic views illustrating the plunger of FIG. 29 as incorporated into other actuator assemblies constructed in accordance with the teachings of the present disclosure.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

With reference to FIGS. 1 through 3 of the drawings, an actuator assembly constructed in accordance with the teachings of the present invention is generally indicated by reference numeral 10. The actuator assembly 10 can include a frame 20, a coil assembly 22, an armature 24, a plunger 26 and a sensor assembly 28.

With reference to FIGS. 4 through 6, the frame 20 can be formed of a suitable material, such as a material having a low magnetic susceptibility (e.g., 316 stainless steel), and can include an outer or first annular sidewall 34, an inner or second annular sidewall 36, an endwall 38 and a sensor mount 40. The endwall 38 can be coupled to the first and second annular sidewalls 34 and 36 so as to define an interior annular recess 42 that is bounded on three sides by the first and second sidewalls 34 and 36 and the endwall 38. The second annular sidewall 36 can define a through-hole 44 and may optionally include a lip portion 46 that extends radially inwardly to somewhat close one side of the through hole 44. The configuration of the sensor mount 40 is tailored to the configuration of the particular sensor assembly 28 employed. In the particular example provided, the sensor mount 40 includes a mounting notch 50, which is formed in the endwall 38 and the first annular sidewall 34, and a mounting aperture 52 that is formed in the endwall 38.

Returning to FIG. 3, the coil assembly 22 can include an outer shell 60, an inner shell 62 and a coil 64. When positioned in the recess 42 of the frame 20, the outer and inner shells 60 and 62 can cooperate to form a core structure 66 that defines an annular coil aperture 68 that is sized to receive the coil 64. The coil assembly 22 can cooperate with the frame 20 to define an armature space 70 in an area that is located radially outward of the coil assembly 22 and inwardly of the first annular sidewall 34.

With additional reference to FIGS. 7 and 8, the outer shell 60 can be formed of a suitable material, such as SAE 1008 steel, and can include an annular body 80 and an annular lip member 82 that can extend radially outwardly from the outer edge of the annular body 80. The annular body 80 can be sized to be received in the annular recess 42 in the frame 20 and can include a coil mount 84 having a pair of threaded apertures 86 and a coupling window 88. The annular lip member 82 can include a chamfered interior edge surface 90. In the example provided, the angle of the chamfer is about 25°.

With reference to FIGS. 3, 9 and 10, the inner shell 62 can be formed of a suitable material, such as SAE 1008 steel, and can include a tubular body 90 and a radially projecting wall 92. The tubular body 90 can be sized to be received within the annular recess 42 and abut the second annular sidewall 36. The radially projecting wall 92 can extend radially from an end of the tubular body 90 so as to abut the first annular sidewall 34. The radially projecting wall 92 can include a first flange portion 94, a second flange portion 96 and a circumferentially extending projection 98 that can be formed between the first and second flange portions 94 and 96 proximate a distal end of the radially projecting wall 92. The circumferentially extending projection 98 can be generally V-shaped, having a first tapered face portion 100, which can intersect the first flange portion 94, and a second tapered face portion 102 that can intersect the second flange portion 96. In the particular example provided, the first tapered face portion 100 is disposed at an angle of about 128° from the first flange portion 94 and the second tapered face portion 102 is disposed at an angle of about 74° from the second flange portion 96.

In FIGS. 3, 11 and 12, the coil 64 can include a coil winding 110, a pair of terminals 112 and a coil overmold member 114. The coil winding 110 can be formed of an appropriate material, such as 168 turns of POLYBONDEX® (polyester/polyaimdeimide/bondcoat) 21 AWG copper wire having a nominal resistance of about 2.9 ohms. It will be appreciated that the turns of the coil winding 110 can be wound about the longitudinal axis of the coil winding 110 in a conventional and well known manner. The terminals 112 can be formed of a suitable conductor, such as 18 AWG Teflon® coated copper wire and can be employed to electrically couple the coil winding 110 to a source of electrical energy (not shown). The terminals 112 of the coil 64 can be fitted through the coupling window 88 (FIG. 7) in the outer shell 60. The coil winding 110 can be fully or partially encapsulated in the coil overmold member 114 to thereby provide the coil winding 110 with structural integrity that permits the coil 64 to be assembled to the remainder of the actuator assembly 10. The coil overmold member 114 can be formed of an appropriate and well known electrically insulating thermoplastic material, such as ZYTEL® HTN 54615 HSLR marketed by E.I. du Pont de Nemours and Company or EpoxySet EC-1012M Epoxicast with an EH-20M hardener mixed at a rate of 100:10.

With reference to FIGS. 3, 13 and 14, the armature 24 can be formed of a suitable material, such as a low carbon steel (e.g., SAE 1008 steel), and can include an annular body 120 and a sensor portion 122. The annular body 120 can include a first end 124, a second end 126, an interior surface 128 and a tapered surface 130 that intersects the interior surface 128 and the second end 126. In the example provided, the first and second ends 124 and 126 are generally perpendicular to the longitudinal axis 132 of the armature 24 and the angle between the tapered surface 130 and the longitudinal axis 132 of the armature is about 16°.

The sensor portion 122 can extend radially outwardly from the annular body 120 and can be disposed about the circumference of the annular body 120. The sensor portion 122 can have first and second surfaces 134 and 136, respectively, that can be oriented generally perpendicular to the longitudinal axis 132 of the armature 24. It will be appreciated that the sensor portion 122 need not be formed in a circumferentially extending manner. For example, the sensor portion 122 could be formed as a single tooth that extends radially from the annular body 120 over only a portion of the circumference of the annular body 120. Configuration in this manner would require corresponding changes to the frame 20, the tubular body 120 and/or the plunger 26 to facilitate the “keying” of the armature 24 to the frame 20 and the armature's 24 movement of the plunger 26.

The armature 24 can be disposed in the armature space 70 and can axially translate within the recess 42 in the frame 20. It will be appreciated that the tapered surface 130 of the armature 24 cooperates with the second tapered face portion 102 (FIG. 10) of the inner shell 62 to permit the armature 24 to axially overlap the inner shell 62 without contacting the core structure 66 along this tapered interface. It will also be appreciated that the second end 126 of the armature 24 will contact the second flange portion 96 (FIG. 10) of the inner shell 62 before the tapered surface 130 and the second tapered face portion 102 (FIG. 10) contact one another so that an air gap will always exist between the tapered surface 130 and the second tapered face portion 102 (FIG. 10).

In FIGS. 3 and 15, the plunger 26 can be formed of an appropriate material, such as a material having a low magnetic susceptibility (e.g., 316 stainless steel), and can be a cap-like structure having a flange member 140 and a side wall or rim member 142. The flange member 140 can be a ring-shaped plate and can include a plurality of circumferentially spaced-apart apertures 144. The rim member 142 can be coupled to the outer radial edge of the flange member 140 and can extend about the circumference of the flange member 140. A plurality of circumferentially spaced-apart apertures 146 can be formed through the rim member 142. The apertures 144 and 146 can be configured to permit the plunger 26 to more easily translate. For example, the apertures 144 and 146 can reduce the mass of the plunger 26 and as such, it will be appreciated that their quantities, shape and size may be selected based on the parameters of a given application. Such design choices are within the ordinary level of skill in the art and as such, need not be explained in detail herein. The circumference of the rim member 142 can be sized so that the rim member 142 can be received in the recess 42 radially outwardly of the core structure 66 and the flange member 140 can be abutted against the core structure 66 on a side opposite the endwall 38 of the frame 20. A distal end 148 of the rim member 142 can abut a portion of the armature 24, such as the first surface 134 (FIG. 14) of the sensor target 122.

Returning to FIGS. 1 and 2 and with additional reference to FIGS. 16 and 17, the sensor assembly 28 can include a back-biased Hall-effect sensor, such as an AT635LSETN-T sensor marketed by Allegro MicroSystems of Worcester Mass. The sensor assembly 28 can include a housing 200 and a sensor portion 202. The housing 200 can be a thermoplastic material that can be overmolded onto the sensor portion 202 and can define a locator 208 (FIG. 2) that can be sized and shaped to matingly engage edges of the mounting aperture 52 (FIG. 4) formed in the endwall 38 and the first annular sidewall 34 of the frame 20. As will be appreciated, the locator(s) on the housing 200 can cooperate with the mounting aperture 52 and other features of the frame 20 to position the sensor assembly 28 in a predetermined location relative to the sensor target 122 (FIG. 3). The sensor assembly 28 can be coupled to the frame 20 in any appropriate manner, such as epoxy bonding or overmolding. Such techniques are well known in the art and as such, need not be discussed in detail herein. In the particular example provided, an overmold 210 is applied to the sensor portion 202 to fixedly couple the sensor portion 202 to the frame 20.

With reference to FIG. 17, the sensor portion 202 can include a circuit 220 and a magnet 222. As will be appreciated, the magnet 222 is operable for producing a magnetic field and the circuit 220 can include a Hall-effect circuit that can be operable for sensing the magnetic field. Positioning of the sensor target 122 (FIG. 3) within the magnetic field can alter the field lines of the magnetic field and these alterations can be sensed by the circuit 220. Accordingly, the circuit 220 can produce a sensor signal that is responsive to a position of the sensor target 122 (FIG. 3). In the example provided, the circuit 220 can switch on and off in response to the position of the sensor target 122 (FIG. 3) relative to the sensor portion 202. The circuit 220 can be a digital, programmable, true-power-on Hall-effect circuit. In this regard, the circuit 220 can provide a first digital switch output (e.g., a low logic level) when the sensor target 122 (FIG. 3) is in a first position and the circuit 220 is in a first state (e.g., corresponding to a high logic level) and a second digital switch output (e.g., a high logic level) when the sensor target 122 (FIG. 3) is in a second position and the circuit 220 is in a second state (e.g., corresponding to low logic level).

The output of the circuit 220 is schematically illustrated in FIG. 18. With additional reference to FIGS. 3 and 17, movement of the sensor target 122 in the direction X when the state condition of the circuit 220 is low does not effect the state condition of the circuit 220 when the sensor target is in-line with the second position 230 and consequently, the circuit 220 continues to output the first digital switch output. Continued movement of the sensor target in the direction X positions the sensor target at the first position 232, which causes the circuit 220 to switch to from a low logic state 226 to a high logic state 228 and the circuit 220 responsively produces the second digital switch output. Thereafter, the sensor target can move further in the direction X or can move toward the second position 230 (but not in-line with the second position 230) without affecting the output of the circuit 220.

When the circuit 220 is in the high logic state and the sensor target is moved in-line with the second position 230, the circuit 220 will switch from the high logic state 228 to the low logic state 226 and the circuit 220 responsively produces the first digital switch output. Thereafter, the sensor target 122 can move further in a direction opposite the direction X or can move toward the first position 232 (but not in-line with the first position 232) without affecting the output of the circuit 220.

With reference to FIG. 19, it will be appreciated that the terminals 112 of the coil 64 can be selectively coupled to a source of electrical power, such as a battery 250. The circuit 220 can include an input terminal 252, which is configured to receive an electrical input of a predetermined voltage, and an output terminal 254 that is configured to transmit the first and second digital switch outputs to a controller 256. A capacitor 258 can be electrically coupled to the input terminal 252 and the output terminal 254 to attenuate electrical noise.

With additional reference to FIG. 3, electrical power can be applied to the coil 64 to actuate the actuator assembly 10, wherein a magnetic field produced by the coil 64 will drive the armature 24 in an actuating direction (i.e., a direction opposite the endwall 38 of the frame 20). As the distal end 148 of the rim member 142 of the plunger 26 is abutted against the first surface 134 of the sensor target 122, translation of the armature 24 in the actuating direction will cause corresponding translation of the plunger 26.

As the circuit 220 of the sensor assembly 28 is programmable in the example provided, the actuator assembly 10 can be positioned in a setting jig or fixture 280 as shown in FIG. 20 between a datum surface 282 and a gauging surface 284 that is spaced apart from the datum surface 282 by a predetermined distance. The actuator assembly 10 can be actuated so that the plunger 26 is extended sufficiently such that a non-moving portion of the actuator assembly 10 (e.g., the frame 20) is abutted against one of the datum surface 282 and the gauging surface 284 while the plunger 26 is abutted against the other one of the datum surface 282 and the gauging surface 284. It will be appreciated that the sensor target 122 will be positioned in a predetermined position (e.g., the first position) and as such, the circuit 220 may be programmed to identify this condition. In the example provided, the circuit 220 is configured such that the setting of one position (e.g., the first position) will automatically set or establish the other position (e.g., the second position).

In view of the above, it will be appreciated that the actuator assembly 10 may be pre-programmed and thereafter assembled to a driveline component, such as a locking differential or a transfer case, without further programming or calibration in certain applications. The pre-programming of the sensor assembly 28 is particularly advantageous in that it permits the programming to be performed prior to the installation of the actuator assembly 10 to the driveline component in an environment where the programming may be performed in a relatively more efficient manner with relatively simple and inexpensive tooling (i.e., tooling that is not based on the configuration of the driveline component). Moreover, pre-programming of the actuator assembly 10 eliminates the need for further programming and/or calibration should the actuator assembly 10 be replaced when the driveline component is serviced.

While the sensor assembly 28 and the sensor portion 202 have been illustrated and described herein as including a back-biased Hall-effect sensor, those of ordinary skill in the art will appreciate that any appropriate type of sensor may be employed in the alternative. For example, the sensor assembly 28 and the sensor portion 202 could include a magnetoresistive sensor or a magnetostrictive sensor, such as a magnetoresistive or magnetostrictive Hall-effect sensor, as such sensors can be somewhat less influenced by a change in the magnitude of the magnetic field proximate the sensor assembly 28. It will also be appreciated that the sensor assembly 28 can include a second sensor portion 202′ as shown in FIG. 20A. The dual sensor portions 202, 202′ provide a level of redundancy that may be desirable in some situations.

With reference to FIG. 21, a motor vehicle 300 is illustrated to include a drive train 302 that incorporates an actuator assembly constructed in accordance with the teachings of the present disclosure. The motor vehicle 302 can include a power source 304, such as an internal combustion engine, and a transmission 306 that can provide rotary power to the drive train 302 in a manner that is well known in the art. In the example provided, the drive train 302 includes a transfer case 312, a first or front axle assembly 314, a second or rear axle assembly 316, a first propeller shaft 318, which conventionally couples the front axle assembly 314 to a front output shaft 320 of the transfer case 312, and a second propeller shaft 322 that conventionally couples the rear axle assembly 316 to a rear output shaft 324 of the transfer case 312. The transfer case 312 can receive rotary power from the transmission 306 and can distribute rotary power to the front and rear axle assemblies 314 and 316 in a desired manner.

The front and rear axle assemblies 314 and 316 can be similar in their construction and operation and as such, only the rear axle assembly 316 will be discussed in detail herein. With additional reference to FIG. 22, the rear axle assembly 316 can include an axle housing 350, a differential assembly 352 and a pair of axle shafts 354 (only one of which is specifically shown). The axle housing 350 can be conventionally configured and can include a housing structure 360 and a pair of bearing caps 362 that can be fixedly but removably coupled to the housing structure 360. The housing structure 360 can define a differential cavity 364 that houses the differential assembly 352. The bearing caps 362 can be decoupled from the housing structure 360 to permit the differential assembly 352 to be received within the differential cavity 364. The axle shafts 354 can be coupled to opposite sides of the differential assembly 352 and to respective ones of the rear vehicle wheels 362 (FIG. 21) in any appropriate manner.

With additional reference to FIGS. 23 and 24, the differential assembly 352 can include a differential case 400, a ring gear 402 (FIG. 22), a gear set 404, a locking system 406 and an input pinion 408 (FIG. 22). The input pinion 408 and the ring gear 402 can be conventionally constructed and mounted in the axle housing 350 and as such, need not be discussed in significant detail herein. Briefly, the input pinion 408 can be coupled to the axle housing 350 via a set of bearings (not specifically shown) and disposed about a rotational axis that is generally perpendicular to a rotational axis of the differential case 400. The input pinion 408 can include a plurality of pinion teeth (not shown) that can be meshingly engaged to a plurality of ring gear teeth (not specifically shown) formed on the ring gear 402.

The differential case 400 can include a body portion 420 and a circumferentially-extending flange 422 that is coupled to (e.g., integrally formed with) the body portion 420. The flange 422 can include a plurality of apertures 424 that can facilitate the removable coupling of the ring gear 402 via a plurality of threaded fasteners 426.

The body portion 420 can define a gear set cavity 430 and one or more assembly windows 432, which can be employed to install the gear set 404 into the gear set cavity 430. In the example provided, the body portion 420 includes first and second side segments 440 and 442, respectively, and first and second end segments 444 and 446, respectively. Each of the first and second side segments 440 and 442 can include a through-bore 448, which can be arranged generally perpendicular to the rotational axis of the differential case 400, and a boss 450 that can be disposed concentrically about the through-bore 448 within the gear set cavity 430. A relatively large fillet radius 452 can be employed at the intersection between the second end segments and the first and second side segments 440 and 442.

Each of the first and second end segments 444 and 446 can span between the first and second side segments 440 and 442 and can include a hollow, axially extending trunnion 450. Each trunnion 450 can define an inside diameter, which can be sized to receive a corresponding one of the axle shafts 354 there through, and an outside diameter that can be sized to engage a bearing 454 (FIG. 22) that is disposed between the housing structure 360 and the bearing cap 362. Those of ordinary skill in the art will appreciate that the differential case 400 may be may be mounted to the axle housing 350 via the bearings 454 for rotation within the differential cavity 364 about the aforementioned rotational axis.

A retaining bore 458 can be formed through the first end segment 444 and a portion of the second side segment 442 and can intersect the through-bore 448. A first annular pocket 460 can be formed in the interior face of the first end segment 444 and can be concentric with the trunnion 450. The first annular pocket 460 can include a first bore portion 462 and a second bore portion 464 that can be concentric with and relatively smaller in diameter than the first bore portion 462.

The second end segment 446 can include an outer portion that defines a mounting hub 470 and an interior portion that defines a second annular pocket 472. The mounting hub 470 can be disposed between the flange 422 and the trunnion 450 and can include an actuator mount surface 480 that can be generally concentric with the trunnion 450. A circumferentially extending groove 482 can be formed in the actuator mount surface 480. A plurality of actuator apertures 484 can be formed axially through the second end segment 446 and can intersect the second annular pocket 472. The second annular pocket 472 can include a pocket portion 490, a plurality of locking features 492 and a thrust ring pocket 494. In the example provided, the pocket portion 490 is generally circular in shape and the locking features 492 can be recesses that can intersect the pocket portion 490. The locking features 492 can be shaped in any appropriate manner and in the example provided, have a half-circle shape that extends from the pocket portion 490. The thrust ring pocket 494 can be circular in shape and concentric with the pocket portion 490.

The gear set 404 can include first and second side gears 500 and 502, respectively, first and second pinion gears 504 and 506, respectively, a cross-shaft 508 and a retaining bolt 510. The first side gear 500 can include an annular gear portion 520, which can have a plurality of gear teeth, an annular hub portion 522, which can intersect the gear portion 520 at a flange face 524, and a splined aperture 526 that can engage a mating splined segment (not shown) formed on a corresponding one of the axle shafts 354. The hub portion 522 can be sized to be received in the second bore portion 464 in the first end segment 444, while a portion of the gear portion 520 can be received in the first bore portion 462. In the particular example provided, a thrust washer 530 is disposed over the hub portion 522 and abuts the flange face 524.

The second side gear 502 can include a gear portion 540, which can have a plurality of gear teeth, a tubular hub portion 542 and a splined aperture 546. The tubular hub portion 542 can axially extend from the second side gear 502 in a direction opposite the gear portion 540. The splined aperture 546 can be formed through the tubular hub portion 542 and can engage a mating splined segment (not shown) formed on a corresponding one of the axle shafts 354. The second side gear 502 can be received in the first pocket portion 490 of the second end segment 446. A thrust washer 560 can be disposed in the thrust ring pocket 494 between the interior surface 562 of the second end segment 446 and an axial end face 564 of the tubular hub portion 542. It will be appreciated that the thickness of the thrust washer 560 can be selected to control the lash between the teeth of the second side gear 502 and the teeth of the first and second pinion gears 504 and 506.

The first and second pinion gears 504 and 506 can be rotatably mounted on the cross-shaft 508 and meshingly engaged to the teeth of the first and second side gears 500 and 502. The cross-shaft 508 can extend through the through-bores 448 in the first and second side segments 440 and 442. Washer-like spacers 470 can be employed to control the lash between the first and second pinion gears 504 and 506 and the first and second side gears 500 and 502. The retaining bolt 510 can be inserted into the retaining bore 458 and threadably engaged to a mating threaded aperture 472 formed in the cross-shaft 508 to thereby fixedly secure cross-shaft 508 to the differential case 400.

The locking system 406 can include a first dog ring 600, a second dog ring 602, a return spring 604, a spacer ring 606, a thrust plate 608, an actuator assembly 10 a and a retaining ring 610.

With reference to FIGS. 23 through 25, the first dog ring 600 can be coupled (e.g., integrally formed) with the second side gear 502 on a portion thereof opposite the gear portion 540. The first dog ring 600 can include a plurality of circumferentially spaced apart radially extending teeth 620 and a circular groove 622 that can be disposed between the tubular hub portion 542 and the teeth 620. In the example provided, the teeth 620 are relatively numerous and shallow so as to provide increased strength and load sharing between the teeth 620 as well as to lower tooth contact stresses.

The second dog ring 602 can include an annular body portion 640, a plurality of mating locking features 642, a circular groove 644 and a pilot portion 646. The annular body portion 640 can be received in the pocket portion 490 of the second annular pocket 472 and can include a plurality of teeth 650 that are configured to matingly engage the teeth 620 of the first dog ring 600. The circular groove 644 can be disposed radially inwardly of the teeth 650 and can generally correspond to the circular groove 482 formed in the first dog ring 600. The pilot portion 646 can be an annular axially projecting rim that can aid in retaining the return spring 604 to the second dog ring 602. Additionally or alternatively, the pilot portion 646 can engage a mating feature formed on the first dog ring 600 or the second side gear 502 that can guide or aid in guiding the teeth 650 of the second dog ring 602 into engagement with the teeth 620 of the first dog ring 600. The mating locking features 642 can be coupled to the annular body portion 640 and in the example provided, comprise tabs that are semi-circular in shape. The mating locking features 642 are configured to engage the locking features 492 in the second annular pocket 472 to permit the second dog ring 602 to be non-rotatably coupled to the differential case 400 but axially movable relative to the differential case 400 along the rotational axis of the differential case 400.

The spacer ring 606 can be disposed within the pocket portion 490 about the locking features 492 and can be positioned axially between the second dog ring 602 and the surface 490 a of the pocket portion 490. The return spring 604 can be any appropriate spring and can bias the first and second dog rings 600 and 602 apart from one another. In the example provided, the return spring 604 is a double wave spring that can be disposed in the circular grooves 622 and 644. It will be appreciated that the return spring 604 can bias the second dog ring 602 into abutment with the spacer ring 606 and the spacer ring 606 into abutment with the second end segment 446.

The thrust plate 608 can include a plate portion 700 and a plurality of leg members 702. The plate portion 700 can have an annular shape and can be sized so as to be slidably received over the actuator mount surface 480. The leg members 702 can be coupled to the plate portion 700 and can extend axially through the actuator apertures 484 formed in the second end segment 446. The end of the leg members 702 opposite the plate portion 700 can engage the second dog ring 602 in an appropriate area. In the example provided, the thrust plate 608 include four leg members 702 each of which abutting a corresponding one of the mating locking features 642.

The actuator assembly 10 a can be generally similar to the actuator assembly 10 described above in conjunction with FIGS. 1 through 19, except that the actuator assembly 10 a includes a bushing 750 and an anti-rotate bracket 752. With reference to FIGS. 26 and 27, the bushing 750 can be formed of an appropriate material, such as an oil-impregnated sintered bronze conforming to ASTM B438. The bushing 750 can have an outer diameter, which can be sized to engage the second annular sidewall 36 via an interference fit. The bushing 750 can be pressed into the annular recess 42 such that an end of the bushing 750 abuts the annular lip 46. The bushing 750 can define an inner diameter that is sized to be journally supported on the actuator mount surface 480 (FIG. 24) of the mounting hub 470 (FIG. 24) of the differential case 400 (FIG. 24).

The anti-rotate bracket 752 can be formed of an appropriate material, such as a material having a low magnetic susceptibility (e.g., 316 stainless steel), and can include one or more tab members 760 that can be coupled to the frame 20. In the particular example provided, the anti-rotate bracket 752 is a discrete structure that includes an annular body portion 762 that can be coupled to the frame member 20 by an appropriate coupling means, such as fasteners (e.g., threaded fasteners, rivets), welds or adhesives. The tab members 760 can extend generally perpendicular to the annular body portion 762 and are configured to engage the opposite lateral surfaces of an associated one of the bearing caps 362 (FIG. 22) so as to inhibit relative rotation between the axle housing 350 (FIG. 22) and the actuator assembly 10 a. It will be appreciated, however, that the tab members 760 could be integrally formed with the frame 20 in the alternative.

Returning to FIGS. 23 and 24, the actuator assembly 10 a can be slidably received onto the mounting hub 470 such that the plunger 26 can be abutted against the plate portion 700 of the thrust plate 608. The snap ring 610 can be received in the circumferentially extending groove 482 in the actuator mount surface 480 and can inhibit axial withdrawal of the actuator assembly 10 a from the mounting hub 470.

When the actuator assembly 10 a is actuated, the plunger 26 will translate the thrust plate 608 such that the leg members 702 urge the second dog ring 602 toward the first dog ring 600 such that the teeth 620 and 650 of the first and second dog rings 600 and 602 engage one another. As the second dog ring 602 is non-rotatably coupled to the differential case 400 and as the first dog ring 600 is non-rotatably coupled to the second side gear 502, engagement of the teeth 620 and 650 inhibits rotation of the second side gear 502 relative to the differential case 400, thereby locking the differential assembly 352 to inhibit speed differentiation between the axle shafts 354 (FIG. 22). It will be appreciated that the tab members 760 of the anti-rotate bracket 752 can contact the sides of the adjacent bearing cap 362 (FIG. 22) to thereby inhibit or limit rotation of the actuator assembly 10 a relative to the axle housing 350 (FIG. 22). It will be appreciated that as the actuator 10 a is immersed in a fluid (i.e., a lubricating and cooling oil), the apertures 144 in the plunger 26 can be sized and shaped to reduce surface tension and friction, while the apertures 146 (FIGS. 15 and 27) in the plunger 26 can form ports for intaking fluid into and exhausting fluid from the armature space 70 (FIG. 27). Additionally or alternatively, the plunger 26 can be configured such that the flange member 140 (FIG. 15) can be spaced apart from the coil assembly 22 by a predetermined distance, such as 0.04 inch (1 mm) when the actuator 10 a is in a non-actuated condition and the plunger 26 is fully returned toward the coil assembly 22. As those of ordinary skill in the art will appreciate, it is commonly understood that the volume of a vehicle component should be minimized to improve the packaging of the vehicle component into a particular vehicle. We have found, however, that the spacing between the flange member 140 (FIG. 15) and the coil assembly 22 can reduce surface tension and friction, particularly at when the temperature of the lubricating oil is relatively cold.

It will be appreciated that as the actuator assembly 10 a is pre-programmed/calibrated, the differential assembly 352 may be assembled and tested (as necessary) without calibrating or programming the sensor assembly 28 after it has been installed to the differential case 400. Moreover, it will be appreciated that as the sensor assembly 28 directly senses a position of the armature 24 (FIG. 27) via the sensor portion 122 (FIG. 27), the sensor signal produced by the sensor assembly 28 can be employed to both identify the state in which the differential assembly 352 is operated (e.g., locked or unlocked) and the position of the armature 24 (FIG. 27). This latter information is significant in that direct sensing of the position of the armature 24 (FIG. 27) permits the controller 256 (FIG. 22) to accurately identify those situations where the armature 24 (FIG. 27) has traveled sufficiently to cause actuation of the differential assembly 352; the controller 256 (FIG. 22) may thereafter alter the manner in which electrical power is provided to the actuator assembly 10 a. For example, the controller 256 (FIG. 19) may utilize a pulse-width modulating technique to provide electrical power to the actuator assembly 10 a. The controller 256 (FIG. 19) can employ a first, relative high duty cycle so that the apparent voltage provided to the actuator 10 a is relatively high to initiate movement of the thrust plate 608 to lock the differential assembly 352. Thereafter, the controller 256 (FIG. 19) can employ a second, relatively lower duty cycle in response to a change in the sensor signal when the sensor target 122 (FIG. 27) is positioned at the first position. In this regard, a relatively lower duty cycle can be employed to hold or maintain the actuator 10 a in an actuated condition. The lower duty cycle provides a relatively lower apparent voltage and reduces energy consumption and the generation of heat by the actuator 10 a.

While the actuators 10 and 10 a of FIGS. 1 and 27 have been described thus far as including an armature with an integral sensor target, those of ordinary skill in the art will appreciate that the actuator, in its broader aspects, may be constructed somewhat differently. For example, the sensor target may be directly coupled to the plunger as shown in FIGS. 29 and 30. In this arrangement, a portion of the side wall or rim member 142 b of the plunger 26 b can be sheared and bent outwardly to form a sensor tab 1000, while the remainder of the plunger 26 b can be configured as described above. A ferro-magnetic target 1002 can be overmolded onto the sensor tab 1000. In the particular example provided, a target aperture 1004 is formed through the sensor tab 1000 and the ferro-magnetic material 1002 is overmolded onto the sensor tab 1000 in a location that corresponds to the target aperture 1004. The ferro-magnetic target 1002 and the sensor tab 1000 cooperate can cooperate to define the sensor target 122 b. A slot 1006 can be formed in the second annular sidewall 36 b of the frame 20 b to receive the sensor tab 1000 and/or the sensor target 122 b when the sensor target 122 b translates axially relative to the frame 20 b. The sensor assembly 28 b can be coupled to the frame 20 b in a manner that is similar to that which is described above and can include any appropriate type of sensor. In the particular example provided, the sensor assembly 28 b includes a back-biased Hall-effect sensor, such as an AT635LSETN-T sensor marketed by Allegro MicroSystems of Worcester Mass. Further examples of suitable sensors include magnetoresistive sensors and magnetorstrictive sensors, which could be Hall-effect type sensors.

The example of FIG. 31 is similar to that which is shown in FIGS. 29 and 30, except that a forward-biasing magnet 1010 is coupled to the sensor tab 1000 rather than the overmolding of a ferro-magnetic material onto the sensor tab 1000. The forward-biasing magnet 1010 can be fitted into the target aperture 1004 and secured to the sensor tab 1000 in any desired manner, such as through adhesives, mechanical couplings and/or overmolding. The sensor assembly 28 c can include a linear hall element 1012 can be coupled to the frame 20 b and can cooperate with the forward-biasing magnet 1010 to identify a position of the plunger 26 c relative to the frame 20 b. The example of FIG. 32 is also similar to that which is shown in FIG. 31, except that the sensor assembly 28 d is a magneto-resistive sensor that is coupled to the frame 20 b. Those of ordinary skill in the art will appreciate that the magnet 1010 can have any appropriate shape.

It will be appreciated that the arrangements of FIGS. 30 through 32 orient the sensor assembly in a manner that is generally perpendicular to an apparent magnetic field of the sensor target. Construction in this manner can help the sensor assembly to be relatively more tolerant of fluctuations in the magnitude of magnetic field of the sensor target.

While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims. 

1. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface that is disposed on a side of the circumferentially extending projection opposite the annular cavity, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; and wherein at least a portion of the tapered face of the circumferentially extending projection is disposed radially in-line with the coil.
 2. The locking differential of claim 1, wherein the electromagnet is fixed to the case and energization of the electromagnet is configured to move the armature.
 3. The locking differential of claim 1, wherein the shell member comprises a tubular body that is coupled to a side of the annular flange opposite the circumferentially extending projection.
 4. The locking differential of claim 1, wherein a second tapered surface is formed on the circumferentially extending projection on a side facing the annular cavity.
 5. The locking differential of claim 1, wherein the coil has a first axial end, which is abutted against the annular flange, and a second axial end opposite the first axial end, and wherein an end of the circumferentially extending projection that is disposed on a side opposite the annular flange terminates between the first and second axial ends of the coil.
 6. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface that is disposed on a side of the circumferentially extending projection opposite the annular cavity, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the electromagnet further comprises a housing that forms a generally U-shaped circumferentially extending channel with an radially inner wall member and a radially outer wall, the shell member being received into the generally U-shaped circumferentially extending channel between the radially inner wall and the radially outer wall.
 7. The locking differential of claim 6, further comprising a sensor that is coupled to the housing, the sensor being configured to produce a sensor signal indicative of the relative positioning of the armature and the housing in at least one position.
 8. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface that is disposed on a side of the circumferentially extending projection opposite the annular cavity, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the electromagnet further comprises a second shell member that is disposed on a side of the coil opposite the shell member, the second shell member having a cylindrical surface onto which the annular body portion is slidably engaged.
 9. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member being formed of a ferrous material and having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the coil has a first axial end, which is abutted against the annular flange, and a second axial end opposite the first axial end; and wherein the tapered surface of the circumferentially extending projection is disposed between the first and second axial ends of the coil.
 10. The locking differential of claim 9, wherein the electromagnet is fixed to the case and energization of the electromagnet is configured to move the armature.
 11. The locking differential of claim 9, wherein the shell member comprises a tubular body that is coupled to a side of the annular flange opposite the circumferentially extending projection.
 12. The locking differential of claim 9, wherein a second tapered surface is formed on the circumferentially extending projection on a side facing the annular cavity.
 13. The locking differential of claim 9, wherein the circumferentially extending projection is spaced radially apart from the coil.
 14. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member being formed of a ferrous material and having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the coil has a first axial end, which is abutted against the annular flange, and a second axial end opposite the first axial end; and wherein an end of the circumferentially extending projection that is disposed on a side opposite the annular flange terminates between the first and second axial ends of the coil; wherein the electromagnet further comprises a housing that forms a generally U-shaped circumferentially extending channel with a radially inner wall member and a radially outer wall, the shell member being received into the generally U-shaped circumferentially extending channel between the radially inner wall and the radially outer wall.
 15. The locking differential of claim 14, further comprising a sensor that is coupled to the housing, the sensor being configured to produce a sensor signal indicative of the relative positioning of the armature and the housing in at least one position.
 16. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member being formed of a ferrous material and having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the coil has a first axial end, which is abutted against the annular flange, and a second axial end opposite the first axial end; and wherein an end of the circumferentially extending projection that is disposed on a side opposite the annular flange terminates between the first and second axial ends of the coil; wherein the electromagnet further comprises a second shell member that is disposed on a side of the coil opposite the shell member, the second shell member having a cylindrical surface onto which the annular body portion is slidably engaged.
 17. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; and wherein the circumferentially extending projection is spaced radially apart from the coil and wherein at least a portion of the tapered face of the circumferentially extending projection is disposed radially in-line with the coil.
 18. The locking differential of claim 17, wherein the electromagnet is fixed to the case and energization of the electromagnet is configured to move the armature.
 19. The locking differential of claim 17, wherein the shell member comprises a tubular body that is coupled to a side of the annular flange opposite the circumferentially extending projection.
 20. The locking differential of claim 17, wherein a second tapered surface is formed on the circumferentially extending projection on a side facing the annular cavity.
 21. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; and wherein the circumferentially extending projection is spaced radially apart from the coil; wherein the electromagnet further comprises a housing that forms a generally U-shaped circumferentially extending channel with a radially inner wall member and a radially outer wall, the shell member being received into the generally U-shaped circumferentially extending channel between the radially inner wall and the radially outer wall.
 22. The locking differential of claim 21, further comprising a sensor that is coupled to the housing, the sensor being configured to produce a sensor signal indicative of the relative positioning of the armature and the housing in at least one position.
 23. A locking differential comprising: a case that is configured to be rotatable about an axis; a gearset received in the case, the gearset comprising a first side gear, a second side gear and a plurality of pinions that are configured to transmit rotary power between the case and at least one of the first and second side gears; a dog clutch that is selectively actuatable to control speed differentiation between the first and second side gears, the clutch comprising a first clutch member and a second clutch member that is coupled to the first side gear, wherein the first clutch member is axially movable along a translation axis that is coincident with the rotational axis between a first position and a second position, the first and second clutch members being engaged to one another when the first clutch member is in the first position, the first and second clutch members being disengaged from one another when the first clutch member is in the second position; an electromagnet comprising a shell member and a coil, the shell member being formed of a ferrous material and defining an annular cavity having a longitudinal axis that is disposed coincident with the translation axis, the shell member having an annular flange, which defines a first end of the annular cavity, and a circumferentially extending projection that extends axially concentric with the longitudinal axis from the annular flange, the circumferentially extending projection comprising a tapered surface, the coil having an annular shape and being received in the annular cavity; and an armature comprising an annular body portion that extends longitudinally about the translation axis, the annular body portion having a mating tapered surface; wherein actuation of the dog clutch is controlled through selective energization of the electromagnet, wherein the tapered surface and the mating tapered surface are configured to lie axially in-line with one another when the first clutch member is moved between the first and second positions, and wherein the tapered surface and the mating tapered surface are configured to lie radially in-line with one another when the first clutch member is in at least one of the first and second positions; wherein the circumferentially extending projection is spaced radially apart from the coil; and wherein the electromagnet further comprises a second shell member that is disposed on a side of the coil opposite the shell member, the second shell member having a cylindrical surface onto which the annular body portion is slidably engaged.
 24. The locking differential of claim 17, wherein the coil is disposed on a side of the annular flange opposite the first clutch member and the gearset. 